Influence of Different Gold-Doped Carbon Electrodes on Interactions with L-Cysteine – a Comparative Study of Glassy Carbon and Paraffin-Impregnated Graphite Electrode

A comparative electrochemical study was conducted to evaluate two gold-doped carbon electrodes: a glassy carbon electrode (GCE) and paraffin-impregnated graphite electrode (PIGE) on their performance to detect interactions between L-cysteine (Cys) and differently sized gold nanoparticles using cyclic voltammetry. The study investigated how the choice of carbon electrode and the size of gold nanoparticles (AuNPs) influence the oxidative response of Cys. Gold, known for its strong affinity toward amino acids, interacts with Cys through both its amino (–NH₂) and thiol (–SH) functional groups, enhancing detection sensitivity, as was shown in our previous study [1] [2]. Different types of carbon electrodes can also directly detect Cys in solution. Their high electrocatalytic activity, attributed to oxygen-containing functional groups and edge-plane graphite sites, facilitates efficient electron transfer. Additionally, their porous structure provides a large surface area, further enhancing detection sensitivity [3]. The stabilization of AuNPs likely depends on the electrode surface properties. The rougher surface of PIGE, offering more adsorption sites, may facilitate stronger attachment of the nanoparticles relative to GCE. Both gold-doped electrodes exhibited a pronounced oxidative response to Cys as compared to the electrodes without gold nanoparticles, confirming their suitability for the interaction detection. The peak potential of gold oxidation remained largely independent of the electrode substrate (GCE or PIGE), suggesting that the underlying carbon material does not significantly affect the thermodynamics of the Au-Cys interaction. The oxidation potential shifted positively with increasing AuNP size, consistent with literature reports [4]. The most significant difference occurred at pH 2 on the gold-doped GCE electrode. The Cys still significantly increased the gold oxidation, but it did not prevent the gold oxide reduction from Au III to Au 0 (reduction peak around 0.45 mV Ag/AgCl ) in contrast to other pH values and the PIGE electrode [5]. This limited inhibition of the gold reduction peak was probably because of a weaker adsorption of the Cys molecules on the surface of the GCE. While both electrodes demonstrated good electrochemical activity, the PIGE provided enhanced sensitivity and better resolution of overlapping peaks, making it more suitable for mechanistic studies. In contrast, the GCE exhibited superior reproducibility and stability of the current response, which is advantageous for quantitative analyses. These findings highlight the importance of electrode material selection and AuNP morphology in optimizing the electrochemical detection of thiol-containing biomolecules such as L-cysteine. References [1] M. Kalantarian, P. Slovensky, et al. Part. Part. Syst. Charact . DOI 10.1002/ppsc.202400230. [2] K. Kudpeng, P. Thiravetyan, Min. Metall. Explor. 2021, 38 , 2185. [3] M. Zhou, J. Ding, L. Guo, Q. Shang, Anal. Chem . 2007, 79 , 14. [4] K. Branina, L. Galperin, E. Vikulova, J. Solid State Electrochem. 2011, 15 , 1049. [5] N. Spãtaru, B. V. Sarada, E. Popa, D. A. Tryk, A. Fujishima, Anal. Chem.2001, 73 , 514 Figure 1

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